50 
Haidaia packardi sp. nov. 
Plate XII, figures 2, 3 
Radial costsD, strong. Tubercles, strongest on a concentric zone 
midway between umbo and base; that is, degenerating before maturity — 
a sign of catamorphism. Tubercles are arranged in concentric series and 
are joined by weak, concentric costae. Costellae, very fine, degenerating 
with maturity to coarse, irregular striae resembling rugose growth lines. 
Inner and marginal carinae strong, coarsely tuberculate. Median carina, 
absent. Furrow, weak. Posterior basal margin has three or four crenu- 
lations on the inside. 
Dimensions. Length, 70 mm.; height, 58; semidiameter, 20. 
Locality. Talus at 3,400 feet on Billhook creek. 
Name. After E. L. Packard, in recognition of his work on west 
American Trigoniae. 
Haidaia statluensis sp. nov. 
Plate XII, figures 4, 5, 6 
Costae weak, though marked by strong, obtuse tubercles that are 
arranged in concentric series and joined by concentric costae. Two figures 
of specially prepared artificial casts are introduced to show this peculiarity, 
which does not appear very plainly on the holotype. Both costae and 
tubercles are small and weak on the umbonal region and anterior end. 
Area marked by faint, transverse striae which become with maturity coarse 
costellae. Carinae not specially marked. Furrow, shallow, becoming 
obsolete with maturity. 
Dimensions. Length, 65 mm.; height, 54; semidiameter, 15. 
Locality. Billhook creek at 3,600 feet. 
Name. Geographical — Statlu creek. 
Genus, Yaadia gen. nov. 
Genotype, Yaadia lewisagassizi sp. nov. 
This genus is instituted for a branch of the pseudoquadrate Trigoniae 
that has a discrepant ornament on the anterior end of the disk, and so can 
not well be included in the true pseudoquadrates, genus Steinmanella nov. 
genotype of which is S. holuhi Kitchin. The discrepant anterior ornament 
of Yaadia is not necessarily any indication of relationship with Scaphi- 
trigon, because this kind of thing might well be developed independently. 
Steinmanella is an Indo-Pacific genus of the early Cretaceous. Yaadia 
is presumably a north Pacific group of the same time. 
Name. From Yaada, Indian legendary name. 
Yaadia lewisagassizi sp. nov. 
Plate XIII, figures 1, 2 
Near the umbo, the two sets of ornament are united into one resemb- 
ling that of Trigonia s.s. The two sets of ornament on the disk are separ- 
ated by a perfectly smooth area. Carinae marked only by rows of coarse 
